Multiple beam (multibeam) phased array antennas are well known and may be employed in a wide variety of applications. One drawback, for example, of a conventional phased array antenna transmitting multiple beams from a common amplifier is that non-linear amplifier characteristics may exist that cause mixing among the signals of each beam port. This produces noise referred to as intermodulation (IM) noise or IM interference. The IM interference from each antenna element may combine coherently across antenna elements, resulting in IM beams that interfere with the reception of the desired beams.
There are various approaches for mitigating IM interference. For example, two approaches are to employ a separate array antenna aperture or a separate amplifier for each beam. However, these approaches result in additional implementation costs, consume additional space, and add to the weight of the overall phased array antenna (factors which may be significant, for example, for aircraft or spacecraft applications).
A third approach is to operate the common amplifier in a more linear region (i.e., an amplifier backoff technique) to reduce IM interference. However, this approach results in a reduction of amplifier efficiency and typically a reduction in power provided by the antenna (or for the same power provided, for example, additional input power must be provided and more heat dissipated). As a result, there is a need for improved multibeam phased array antenna techniques.